The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Fibre optical cables are increasingly replacing copper based cables for use in transmitting data and voice services, such as internet access, telephone services and the like. In order to obtain best efficiency in changeover of such services to be fibre-optic based, the required cable infrastructure is normally installed on a large scale—cabling being installed, at least at street level, for whole streets at a time. This reduces the need for digging up roads etc a number of times as once the core cabling is present, in order to connect a new user, it is simply necessary to run a link from the main cable to the particular location to which the service is to be delivered. This may be done using conventional cable pulling techniques or other established means such as blowing under air pressure specially adapted cables through pre-installed ducts.
In order to facilitate the connection operations, the core cabling is typically routed between cable management enclosures located at regular intervals or as necessary along the cable run. These are weatherproof/watertight enclosures, typically located in manholes, access pits, slot boxes, sewerage systems or at the top of telegraph poles, in which the core cable may typically be diverted/spurred, looped, and then tracked back in its path along the street. The loop of the cable which is contained within the enclosure is protected from the environment and the protective outer sleeving can be removed, exposing the cable bundles located therein. These individual cable bundles and individual fibres thereof can then be managed for simple storage, splicing, splitting and the like, as required in order to meet customer requirements. For example, to provide fibre based services to a new location, an engineer will simply remove the cover to access the interior of the enclosure and then carry out the necessary operations on the fibres exposed therein (splicing, splitting) etc to connect the fibre based infrastructure to the required location.
As illustrated in prior art document WO97/32231, it is known in the art to manage the fibre bundles and fibres within the enclosure by use of splice cassettes hinged on a back plate which in turn are mounted on a support frame so as to be slidable thereon. A number of different splice cassettes are available for performing different operations (single element splicing, single circuit splicing, storage, splitting, etc). The assembly is modular, so that the engineer can select the back plate and cassette combinations required to suit the technical requirements of any particular enclosure.
Once the main outer protective sleeving is removed from a cable, the cable will usually be separated into smaller bundles, each separate sub-bundle being surrounded by its own protective sleeve. If there is no immediate requirement for the individual fibres of any of the bundles or some are being left unbroken in a looped installation for the fibres to be spliced and distributed elsewhere, these bundles will usually simply be coiled up to minimise the space they take up within the enclosure and stored in a dedicated storage area, typically (but not exclusively) on the rear of the tray support frame. Others of the bundles will be separated into their individual fibres by removing the protective sheathing to expose the fibres. In order to protect the exposed fibres, longitudinally extending cable passageways are provided on each side of each fibre management back plate, the exposed fibres being routed into the passageways for directing them along the back plate(s). Each back plate is furthermore provided with guide tracks, formed by spaces between guide projections formed on the back plates, which extend across each back plate between the passageways located on either side. These tracks are used to guide the individual fibres as they are tracked out of the passageways and across the back plate to a cassette mounted thereon for management and splicing purposes. The tracks operate to protect the individual fibres from damage as they extend across the back plate, ensuring that their minimum bend radius is not exceeded as they transition from the passageway to the track, and also helps to keep them tidy.
In the prior art, the guide tracks are configured to provide a curved entry path extending from the tunnel so as to control the minimum bend radius of the fibres. As shown in FIG. 2b of WO97/32231, this is achieved by configuration of the guide projections so that each track extends along a curved path, curving upwards towards the top of the back plate. This arrangement works fine for routing fibres out of or into a passageway coming from or directed towards the top of the back plate. However, it prevents a fibre being routed from a cassette at the bottom of the back plate to a cassette mounted higher up—the asymmetrical curving of the track would mean that a fibre would have to be bend through a very sharp angle in order to track from the bottom of the back plate into one of the back plate passageways.